The present invention relates in general to flexible, annular cutting mats, and in particular, to boltless cutting mats for use with rotary anvils.
Rotary die cutting machines are utilized to perform cutting operations in numerous industries. For example, the corrugated industry utilizes rotary die cutting machines to cut and score corrugated paperboard materials for constructing packaging products such as boxes and shipping containers. Basically, these machines pass a continuously moving workpiece through the nip of a cutting roller and a rotary anvil. The roller includes blades that project from the surface thereof, to provide the desired cutting actions to the workpiece. The rotary anvil includes several cutting mats aligned axially about the anvil surface to support the workpiece at the point where the work material is scored by the blades of the roller. The cutting mats serve as a backstop allowing the blades to be urged against the workpiece without damaging the blades themselves.
During use, the blades on the roller penetrate the cutting mats. This leads to eventual fatigue and wear of the cutting mats, requiring that the cutting mats be periodically replaced. In an effort to more evenly distribute the wear across the cutting mats, rotary anvils are known to oscillate in a lateral direction. The oscillatory action assists in preventing the cutting blades from repeatedly striking the cutting mats in the same location thus extending cutting mat life. However, even with an oscillating anvil, it is unlikely that all of the cutting mats will wear evenly and cutting mats will still have to be periodically replaced. For example, at times, rotary die cutting machines operate on a workpiece such that the full width of the rotary die cutting machine is not used. Under this circumstance, certain cutting mats experience most of the wear. As the cutting mats wear, the quality of the cutting operation deteriorates.
Rotating the relative positions of the cutting mats on the rotary anvil such that the cutting mats wear more evenly may prolong the serviceable life of cutting mats. However, repositioning the cutting mats causes downtime because the rotary die cutting machine cannot be in operation when changing or adjusting the cutting mats. Because of downtime, the industry tendency is to prolong the time between cutting mat changeovers. This can lead to a greater possibility of poor quality cuts.
A number of factors other than cutting mat wear also affect the performance of cutting operations. For example, a rotary anvil typically includes an axially extending channel along the surface thereof. The cutting mats are provided as blankets having flanges along opposite ends of the mat. The cutting mat is wrapped about the cylinder of the rotary anvil and secured thereto by installing the flanged ends into the axial channel. The cutting mats thus create a seam that extends axially along the anvil.
Certain rotary anvils, especially those anvils that have seen extensive service life, can exhibit non-uniform wear, such as beveling of the channel edges. Also, in some operating environments, the dimensions of the channel have been intentionally modified for user specific purposes. Likewise, not all cylinders are made with identical channel dimensions. These inconsistencies in channel dimension can affect how securely the cutting mat is secured to the anvil and thus affect cutting mat performance. For example, diagonally oriented knife blades can tend to act as a wedge when striking at or near the seam between the ends of the cutting mat. Moreover, the oscillatory action of the anvil can exert lateral forces on the cutting mat enhancing the wedge effect. Should the cutting mat skew or shift, for example, because of an imprecise fit with the channel of the anvil, a gap may be created. This can cause damage to the knife blade should the blade strike the anvil in the gap.
Further, the orientation of the cutting blades, especially when positioned axially, can at times, strike the cutting mats along the seam. As a consequence, a cutting blade may slip through the seam possibly damaging the blade. For example, if a cutting blade is positioned along an axial dimension of the roller, the blade can strike the rotary anvil along the axial seam defined between opposite ends of one or more cutting mats. A die cutting machine must exert increased pressure to achieve a satisfactory cut when the blades of the roller slip between the seams defined by or between cutting mats. This increased pressure may shorten the life potential of the cutting mat, may lead to damage of the blade, and may require more frequent maintenance of the roller.